Summary: S100beta is an acidic, metal-binding protein (91 residues) which is expressed in high concentrations (10-20microM) in normal glial cells. It is of clinical interest that patients with Alzheimer disease and Down syndrome have 10 to 20-fold higher than normal concentrations of S100beta. Intracellular S100beta (which is in the reduced form) is known to regulate phosphokinase C-dependent growth processes in glial cells. Extracellular (S100beta)2 (which is an oxidized disulfide linked dimer) is known to induce neurite outgrowth from embryonic neurons. A series of nuclear magnetic resonance (NMR) experiments are currently underway which will provide the high resolution 3-dimensional structure for reduced S100beta. We intend to build upon the resonance assignments obtained for the apo-S100beta, extending these assignments to the S100beta-Ca(II) and -Zn(II) metal ion bound forms. Presumably many of the assignments of tie apo-S100beta will be directly transferable to the S100beta metal-bound complexes. Thus, the resonance assignment process and the solution structure determination of the S100beta-metal complexes should be completed in a timely manner. The solution structure for the oxidized dimer (S100beta)2, and its corresponding Ca(II) and Zn(II) complexes are also planned. Again, these studies will be greatly facilitated by the knowledge of the reduced S100beta structures. As a result, we will define the conformational requirements for neurite growth and neuronal survival activities induced by the (S100beta)2-metal complexes. The conformation of reduced S100beta may be important for delineating the function of S100beta in glial cell growth. Based on the structures determined for the S100beta and (S100beta)2 complexes, the function of specific amino acid residues will be tested using site-directed mutagenesis as described previously. Justification of Relevance: The structural determination in solution of S100beta and its various complexes could elucidate the mechanism of interaction of this brain protein with intra- and/or extracellular targets important for signal transduction and the regulation of cellular processes in the nervous system. Thus, based on structural information obtained from these studies, inhibitors of S100beta-mediated processes may be designed. These drugs could possibly control effects resulting from improperly controlled processes such as gliosis and/or neurite proliferation in Down syndrome and Alzheimer disease patients.